Which PA Power Amplifier should you choose for your PA Speakers?

by Andrew Bishop

You will hear people tell you that a power amplifier needs to be double the speaker power but take care as it depends on what ratings you are reading! Read below.

Here is a quick guide to ensure your power amplifier matches your speakers and is the correct type of amplifier to give the power needed when the occasion or music asks for it.

First a quick reminder on power ratings:

  • RMS or AES or Continuous is the exact rating of the speaker – RMS = route means squared and AES = Audio Engineering Society who publish a standard for the measurement of PA speakers which is generally a 2-hour test using pink noise at a constant level.
  • Program Power is a figure that is double the RMS/AES. Program power is often used in the USA but the UK prefer RMS. I guess Americans like thing bigger especially the numbers! 
  • Peak Power is 4 x RMS/AES and Double the Program power. You will see PMPO or Peak Power printed on colour packaging on speakers made for Car Audio, consumer products and some brands like Alto and Mackie where getting the sale is more important and innocent buyers who are not informed often take the bait.

Therefore, if RMS is 100w, Program Power is 200w and Peak Power is 400w:

RMS is the real pro-audio figure to concentrate on

PROGRAM Power is double the RMS

PEAK Power is double the PROGRAM Power

Suppliers tell the customer to buy amplifiers that are double the power of the speaker because most professional PA Power amplifiers are rated in RMS and speakers are often rated in Program Power.

Finally in this section, note that “RMS power” and “watts RMS” are actually misnomers. “RMS power” is a commonly accepted shorthand that’s become synonymous with continuous power, and most manufacturers use these terms interchangeably.

5 Things to consider when buying a PA Speaker Power Amplifier

  1. Match the Power Rating to your PA speaker Rating – match RMS with RMS, Program with Program, Peak with Peak.
  2. Headroom is fine but do not overdrive your speakers or you will hear them fart and you could blow the drivers. If you have a bigger amp than the speakers go easy on the volume.
  3. Check your impedance. Power amplifiers are happy with 8 ohm and 4-ohm loads and some handle 2 ohm but at 2-ohm musicality can suffer.
  4. 18” ferrite subwoofers take some power so look for class AB or class H amp for subwoofers and these amps carry huge power banks of capacitors and/or toroidal transformers that store energy so when the fast drum n bass music calls for a repetitive punch you dan deliver it.
  5. Class D is great for full-range speakers and mid-top. If you want musicality then the BishopSound BP2k, BP4k and BP44k amplifiers are the best value and the most reliable on the market today.

Some definitions and a final word:


The industry says, buy a PA power amplifier that can deliver power equal to twice the speaker’s program power rating. This means that a speaker with a “nominal impedance” of 8 ohms and a program rating of 350 watts will need a power amplifier that can deliver 700 watts into an 8-ohm load. For a stereo pair of speakers, the amplifier should be rated at 700 watts per channel into 8 ohms.


Extra “headroom” will help you so that only clean, undistorted signal gets to your speakers. Headroom is the difference between the normal operating level of an amplifier, and the maximum level that the amp can pass without distorting. Music has wide variations in dynamic range; without enough headroom, you could find that your gear will clip and distort


BishopSound amplifiers feature a built-in limiter for maximizing signal levels while preventing distortion and preventing overload in a signal, setting a maximum volume level protecting speakers and amplifiers from clipping.

Finally, a word from one of the BishopSound customers:

“My full system normally consists of 3 sets of 802s, the main FOH being two stacked on top of themselves on tripods 10 metres apart and a satellite pair a further 20 metres apart. The bottom end is taken care of by some dB technologies subs, a QL152 and a Sub15D”.

“I am liking the sheer musicality of the BishopSound amplifiers.  The immediacy of the presentation shines at whatever volume, which is no mean feat.  Also, it sounds very even-handed.

Thank you, Mr Bishop, and your team.  You have got a great product and I look forward to using more of them in anger very soon”.

Email today at andrew@bishopsound.com or message us using our Live Chat for more info.